The re-election of Northern Ireland First Minister Mr David Trimble last November was "invalid", the British House of Lords was told today.
The Democratic Unionist Party is challenging the election of Mr Trimble and Mr Mark Durkan as Deputy First Minister, claiming they took place outside a designated six-week period.
The DUP also opposes the decision of Northern Ireland Secretary Dr John Reid not to call fresh Assembly elections before May next year, despite the lateness of the First Minister's election.
Mr John Larkin QC, representing DUP deputy leader Mr Peter Robinson, told five Law Lords: "If, as we say, the election was invalid, those offices are invalidly filled."
The Northern Ireland Secretary's decision to hold the next Assembly elections in May 2003 was "founded on illegality", he said.
The five Law Lords - Lords Bingham, Hoffmann, Hutton, Hobhouse and Millett - were told that Mr Trimble resigned last July in a move to put pressure on the IRA to begin disarming.
Deputy First Minister Mr Seamus Mallon was also forced to step down. Once the IRA had made its next move on decommissioning weapons, Mr Trimble and Mr Durkan went before the Assembly seeking election.
The required cross-party support was not achieved on the first vote but was met a few days later, November 6th, after the designated time-frame, when some Assembly members reclassified themselves as unionist.
At the time, the Northern Ireland Secretary said there was no need for him to call fresh elections, outraging the DUP.
Mr Larkin said some journalists had described the decision taken by Assembly members to reclassify themselves as unionist as a "fudge".
He added: "What happened here was tactical for the purposes of ensuring the election of these offices."
In December last year the High Court in Northern Ireland dismissed an application by the DUP for a judicial review into the election of Mr Trimble. The DUP appealed to Northern Ireland's Court of Appeal against this decision but this was also dismissed in March this year.
PA